"[M]ost consensus forecasts were wrong, often substantially," they found. "And although consensus forecasts improved over time as more information became available, accuracy remained an issue even several years post‐launch."

Some findings:

"More than 60% of the consensus forecasts in our data set were either over or under by more than 40% of the actual peak revenue."

"Although the overall median of the data set was within 4%, the distribution is wide for both under‐ and overestimated forecasts."

"A significant number (53) of consensus forecasts were overly optimistic by more than 160% of the actual peak revenues of the product."

"The variance in peak sales estimates was still 45% versus actual peak sales 6 years after the drug has launched, reflecting continued uncertainty even as new information becomes available."

To sum it up, drug forecasters tend to be wrong by a wide margin, overly optimistic, and persistently wrong even years after the drug is launched.